Haze formation mechanism and prevention proposal for ArF photomask: a study combining simulation and experiment

Haze growth on photomask has emerged as a critical challenge for both photomask suppliers and wafer fabs. The contributing factors are multifaceted, encompassing production environment condition, manufacturing process, raw materials and many other variables. Despite extensive studies have been conducted within the industry and laboratories, the causal relationship between haze formation and its contributing factors remains poorly established, and the underlying mechanism of haze is not yet clearly defined. To address this complex issue, this study proposes a computational model based on empirical haze observation data, aiming to: (1) elucidate the fundamental formation mechanisms through multiscale simulation, and (2) derive actionable contamination prevention strategies. As an application example, through assumption, derivation and calculation of the crystal structure of Haze, several types of anionic polymolybdate structure of haze had been obtained. A multiscale computational model with integration of molecular dynamics (MD) and density functional theory (DFT) was developed, featuring a tripartite model (environmental/ oxide/MoSi layers). The migration behavior of Haze-related cations and anions on the photomask was simulated and observed by adjusting the factors influencing haze occurrence, and the formation response of haze was studied through calculation. This MD model significantly analyzed the influence of different variables on the formation mechanism of Haze. In addition, based on the analysis of the simulation data, a new suggestion was proposed, forming an oxide layer on the MoSi layer with surface modification which could reduce the surface energy as to prevent haze generation, and the possible optimal parameter (density, thickness and surface functional group type) of such oxide layer were obtained. This study constructed a haze occurrence model through simulation, opening up and introducing new ideas for the exploration and research of haze occurrence mechanisms and prevention.